This project concerns clinical and pre-clinical studies of anti-cancer drugs. Using a previously developed assay for citrovorum factor and 5'methyltetrahydrofolate, the distribution of these compounds in plasma and cerebrospinal fluid in man and in primates has been elucidated. The mechanism of methotrexate excretion from CSF in man has been further explored. In vitro evaluation of the relative cytotoxicity of methotrexate and methotrexate in the presence of probenecid has been performed. DNA damage and repair following exposure to intercalating agents including light-sensitive compounds (psoralens) have been further explored. Characteristics of drug-DNA complexes for both psoralen derivatives and for diacridines have been measured. An in vitro tumor cell clonig technique has been explored with regard to the growth of various kinds of tumors and the excretion of known tumor cell markers.